Re: FAILED: Patch "net: macb: Fix tx/rx malfunction after phy link down and up" failed to apply to 6.12-stable tree

[Alexander Dahl <ada@thorsis.com>]

Hello Sasha,

Am Sat, Feb 28, 2026 at 08:28:05PM -0500 schrieb Sasha Levin:
> The patch below does not apply to the 6.12-stable tree.
> If someone wants it applied there, or to any other stable or longterm
> tree, then please email the backport, including the original git commit
> id to <stable@vger.kernel.org>.

I tried cherry-pick the upstream commit
bf9cf80cab81e39701861a42877a28295ade266f on top of v6.12.74 (current
state of the linux-6.12.y branch) and it produced no conflicts.
In fact the diff is very much the same as below, so I'm a little
puzzled why it failed at your side?

I'd like to see this fix in 6.12 stable, because it fixes an actual
problem for us (see msg ids below [1] [2]).  How to proceed here?
E-mail as suggested above?

Greets
Alex

[1] <20260219-knapsack-thirteen-7d9e83451a40@thorsis.com>
[2] <20260219-raffle-unvisited-891b68df5aef@thorsis.com>

> 
> Thanks,
> Sasha
> 
> ------------------ original commit in Linus's tree ------------------
> 
> From bf9cf80cab81e39701861a42877a28295ade266f Mon Sep 17 00:00:00 2001
> From: Kevin Hao <haokexin@gmail.com>
> Date: Sun, 8 Feb 2026 16:45:52 +0800
> Subject: [PATCH] net: macb: Fix tx/rx malfunction after phy link down and up
> 
> In commit 99537d5c476c ("net: macb: Relocate mog_init_rings() callback
> from macb_mac_link_up() to macb_open()"), the mog_init_rings() callback
> was moved from macb_mac_link_up() to macb_open() to resolve a deadlock
> issue. However, this change introduced a tx/rx malfunction following
> phy link down and up events. The issue arises from a mismatch between
> the software queue->tx_head, queue->tx_tail, queue->rx_prepared_head,
> and queue->rx_tail values and the hardware's internal tx/rx queue
> pointers.
> 
> According to the Zynq UltraScale TRM [1], when tx/rx is disabled, the
> internal tx queue pointer resets to the value in the tx queue base
> address register, while the internal rx queue pointer remains unchanged.
> The following is quoted from the Zynq UltraScale TRM:
>   When transmit is disabled, with bit [3] of the network control register
>   set low, the transmit-buffer queue pointer resets to point to the address
>   indicated by the transmit-buffer queue base address register. Disabling
>   receive does not have the same effect on the receive-buffer queue
>   pointer.
> 
> Additionally, there is no need to reset the RBQP and TBQP registers in a
> phy event callback. Therefore, move macb_init_buffers() to macb_open().
> In a phy link up event, the only required action is to reset the tx
> software head and tail pointers to align with the hardware's behavior.
> 
> [1] https://docs.amd.com/v/u/en-US/ug1085-zynq-ultrascale-trm
> 
> Fixes: 99537d5c476c ("net: macb: Relocate mog_init_rings() callback from macb_mac_link_up() to macb_open()")
> Signed-off-by: Kevin Hao <haokexin@gmail.com>
> Cc: stable@vger.kernel.org
> Link: https://patch.msgid.link/20260208-macb-init-ring-v1-1-939a32c14635@gmail.com
> Signed-off-by: Paolo Abeni <pabeni@redhat.com>
> ---
>  drivers/net/ethernet/cadence/macb_main.c | 11 +++++------
>  1 file changed, 5 insertions(+), 6 deletions(-)
> 
> diff --git a/drivers/net/ethernet/cadence/macb_main.c b/drivers/net/ethernet/cadence/macb_main.c
> index 6511ecd5856bd..4ebb40adfab37 100644
> --- a/drivers/net/ethernet/cadence/macb_main.c
> +++ b/drivers/net/ethernet/cadence/macb_main.c
> @@ -705,14 +705,12 @@ static void macb_mac_link_up(struct phylink_config *config,
>  		if (rx_pause)
>  			ctrl |= MACB_BIT(PAE);
>  
> -		/* Initialize rings & buffers as clearing MACB_BIT(TE) in link down
> -		 * cleared the pipeline and control registers.
> -		 */
> -		macb_init_buffers(bp);
> -
> -		for (q = 0, queue = bp->queues; q < bp->num_queues; ++q, ++queue)
> +		for (q = 0, queue = bp->queues; q < bp->num_queues; ++q, ++queue) {
> +			queue->tx_head = 0;
> +			queue->tx_tail = 0;
>  			queue_writel(queue, IER,
>  				     bp->rx_intr_mask | MACB_TX_INT_FLAGS | MACB_BIT(HRESP));
> +		}
>  	}
>  
>  	macb_or_gem_writel(bp, NCFGR, ctrl);
> @@ -2954,6 +2952,7 @@ static int macb_open(struct net_device *dev)
>  	}
>  
>  	bp->macbgem_ops.mog_init_rings(bp);
> +	macb_init_buffers(bp);
>  
>  	for (q = 0, queue = bp->queues; q < bp->num_queues; ++q, ++queue) {
>  		napi_enable(&queue->napi_rx);
> -- 
> 2.51.0
> 
> 
> 
> 
>